29 CFR Part 1630, Regulations to Implement the Equal Employment Provisions of the ADA (Title I Regulations with amendments issued through May 2016)

(ii) Consideration of facts such as condition, manner, or duration may include, among other things, consideration of the difficulty, effort, or time required to perform a major life activity; pain experienced when performing a major life activity; the length of time a major life activity can be performed; and/or the way an impairment affects the operation of a major bodily function. In addition, the non-ameliorative effects of mitigating measures, such as negative side effects of medication or burdens associated with following a particular treatment regimen, may be considered when determining whether an individual's impairment substantially limits a major life activity.